The present disclosure relates generally to the field of floating petroleum drilling and production systems. More specifically, the disclosure relates to methods and systems for lubricating seal elements in a riser slip joint and containing leakage that may occur in a seal element used in such slip joints.
Floating structures are known in the art for drilling wellbores in Earth formations located below the ocean floor, and for producing petroleum from such wellbores. The wellbores are typically drilled using fluid pressure control equipment, called a “blowout preventer” (BOP) affixed to the top of a casing cemented into a relatively shallow portion of the wellbore. A “riser”, which is a pipe formed from segments coupled end to end, is affixed to the top of the BOP and extends therefrom to the floating platform. The riser may provide a conduit for fluids to move from the wellbore upwardly to the floating platform. Therefore a riser as used in wellbore drilling may form a conduit for drilling fluid and drill cuttings to be returned to the floating platform for processing and recirculation into the wellbore.
A riser is assembled to the wellbore from the floating platform by coupling together segments, called “joints” of riser, and moving the assembled “string” of joints of riser downward from the floating platform as successive riser joints are coupled to the string on the platform. The foregoing procedure continues until the riser is long enough to reach the wellbore from the floating platform, whereupon the lowermost end of the riser is coupled to the BOP.
For floating drilling platforms, a slip joint may be used between the upper end of the riser where it terminates on the platform and a fixed portion of the riser which terminates at a selected depth below the drilling deck of the floating drilling platform. The slip joint enables the riser length to change as the floating drilling platform changes with changes in elevation of sea level. A typical slip joint includes an outer pipe and an inner pipe that extends at least partway into the outer pipe. The inner pipe and the outer pipe are enabled to move axially with respect to each other. Typically, the outer pipe is connected to the upper end of the section of riser that extends to the BOP. The inner pipe moves within the outer pipe and is connected at its upper end to the floating drilling platform. Thus, the inner pipe moves up and down with the floating drilling platform. An annular seal may be provided between the inner pipe and the outer pipe to prevent escape of fluid from the annular space between the inner pipe and the outer pipe. It will be recognized by those skilled in the art that the respective placement and movement of the inner pipe and the outer pipe may be reversed from the configuration described above. An example of such a slip joint is disclosed in U.S. Pat. No. 8,973,674 issued to Leuchtenberg.
It has been observed that in slip joint and annular seal systems known in the art, the seal life may be limited because the seal tends to wipe the inner pipe's outer surface dry as it is extended outward from the annular seal. Seal failure is also known in the art. Either of the foregoing may result in spillage of drilling or other fluid disposed in the riser, creating an environmental hazard.
What is needed is an improved method and system to extend the life of an annular seal used in a riser slip joint and to prevent spillage into the sea of any fluid which may leak from a failed annular seal.